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ESR Measurements (esr + measurement)
Selected AbstractsThermal stability study of conductive polyaniline/polyimide blend films on their conductivity and ESR measurement,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2002Moon Gyu Han Abstract Conductivity stability at thermal environment of conductive polyaniline-complexes/polyimide (PANI-complexes/PI) blends, which were doped by camphorsulfonic acid (CSA) and dodecylbenzenesulfonic acid (DBSA), respectively, were investigated by conductivity measurements, electron spin resonance (ESR) spectra, differential and scanning thermometer (DSC). In the conversion process of PANI/Polyamic acid (PAA) to PANI/PI, the blend endeavored some kinds of alteration such as decomplexation of moisture and solvent, dissociation of dopant, crosslinking of PANI chain, and the imidization of PAA chain. PANI-DBSA/PI showed higher thermal stability of conductivity than PANI-CSA/PI, and both samples showed nearly linear decay of conductivity with increasing temperature showing greatly enhancement of conductivity stability. When they were exposed at near or over glass transition temperature, the conductivity decay became faster. The conductivity stability at base environment was also higher for PANI-DBSA/PI due to difficulty in accessing of hydroxyl ion to PANI, which were resulted from dopant. DBSA-doped blends showed increased polaron mobility and concentration at relatively high temperature, which led to extremely higher conductivity and its stability at high temperature. Copyright © 2002 John Wiley & Sons, Ltd. [source] Crystal growth and magnetic properties of the copper coordination polymer [Cu(µ -C2O4)(4-aminopyridine)2(H2O)]nCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2007A. V. Prokofiev Abstract In this paper, we consider various ways of crystal growth of the polymer [Cu(µ -C2O4)(4-aminopyridine)2(H2O)]n. Single crystals of the size of 1.5×1.5×0.2 mm3 have been grown by a slow diffusion technique from solutions of the monoammine copper complex and of the mixture of potassium oxalate and aminopyridine with the stoichiometric ratio. Magnetic susceptibility and ESR measurements have been performed on single crystals large enough for investigating anisotropic properties. The susceptibility can be well described within the model of a Heisenberg antiferromagnetic spin chain. The magnetic measurements reveal a small concentration of paramagnetic moments reflecting the high quality of the single crystals. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Cover Picture: Spectroscopic and Photophysical Properties of a Highly Derivatized C60 Fullerol (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 1 2006Mater. Abstract The photo-oxidative stress in aqueous milieus can readily be generated in the presence of newly synthesized highly derivatized fullerenes (fullerols) reported in the Full Paper by Vileno and co-workers on p.,120. Their basic structural and photophysical properties were characterized using a range of methods, including X-ray photoelectron and IR spectroscopies, and electron spin resonance. Moreover, a significant drop of the local stiffness of a living cell was monitored using atomic force microscopy. This cell softening was attributed to the early effects of the photo-oxidative stress. Hydroxylated C60 molecules, also called fullerols, are a class of water-soluble fullerenes. Here we report the synthesis in acidic conditions of a highly derivatized fullerol (up to 36 carbons per C60 are oxidized). Spectroscopic investigations (X-ray photoelectron spectroscopy and infrared absorption) highlight the coexistence of both acidic and basic forms for the hydroxyl addends of derivatized C60. pH titrimetry reveals that, at millimolar concentrations, only ten protons per fullerol molecule are labile. Such a low value, as compared to 36 hydroxyl groups, is explained by the formation of clusters. A UV-vis absorption study performed over a large range of concentrations also points to the aggregation phenomenon. Moreover, this study shows that the clusters of fullerols appear at relatively low (micromolar) concentrations. An electron spin resonance (ESR) study, based on the attack of singlet oxygen (1,g) on 2,2,6,6-tetramethyl-4-piperidinol (TMP-OH), has proved the potential of hydroxylated C60 for performing efficient generation of singlet oxygen in aqueous solution. ESR measurements, which allow detection and quantification of 1,g, have also revealed the generation of reactive oxygen species (ROS). The yield of generation of 1,g and ROS is strongly correlated to the concentration of fullerol, thus also pointing to the aggregation of fullerol molecules. Exposing glioblastoma cells to oxidative stress in the presence of hydroxylated C60 and visible light has also been performed. Atomic force microscopy is used to monitor the relevant diminishment of the Young's modulus values for cells exposed to the oxidative stress. These results point to a possible application field of fullerols for performing bio-oxidations. [source] Reactions of CH3O2 radicals on solid surfaceINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2004L. A. Manucharova The reaction probability of CH3O2 radicals with NO2, CH4, C3H6, and CH3CHO on the solid surface of KCl in flow at low pressure and temperature range of 297,353 K has been studied. The chosen conditions allowed excluding homogeneous interaction of radicals. The heterogeneous radical decay of peracetic acid served as a source of CH3O2 radicals. On the basis of ESR measurements of CH3O2 radicals with the above-mentioned compounds, a heterogeneous reaction mechanism has been identified. The reactivity of NO2 was greatest for the compounds studied. The effective activation energy was evaluated to be 10.4 ± 0.8 kJ/mol for the reaction of RO2 radicals with NO2 and ,21.3 ± 2.8 kJ/mol for methane. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 591,595, 2004 [source] Synthesis, characterization and ESR measurements of CoNiO nanoparticlesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2005Y. Köseo Abstract Powders of cobalt core with a nickel (II) oxide shell (CoNiO) have been studied by Electron Spin Resonance (ESR) technique in the temperature range of 10,300 K. A strong and broad (1300 G) single ESR peak in X-, K- and Q-band spectra has been observed at all the temperature ranges. While the resonance field remains almost constant, both the ESR line intensity and the line width were seen to increase first slowly down to Tc = 160 K. And then both the resonance field and the ESR signal intensity decrease and the line width increase with decreasing temperature. Below Tc the intensity smoothly decrease down to 10 K. This kind of behavior is attributed to a typical spin-glass like behavior. Some small and relatively smooth changes at about 60 K, 90 K, 210 K, and 250 K are appeared as well. A linear dependence of resonance field to microwave frequency is observed at room temperatures and the effective g-value and internal field are theoretically found as 2,17 and 90 G, respectively. The experimental data indicate a very strong spin disorder (spin frustration) due to antiferromagnetic exchange interactions among the spins. This is attributed to the D-M anisotropy on the particle surfaces that it is expected to enhance due to increment of surface-to-volume ratio. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] ESR studies on superparamagnetic Fe3O4 nanoparticlesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004Y. Köseo Abstract In this study we have investigated temperature and frequency dependence of magnetic properties of superparamagnetic iron oxide nanoparticles (SPION). ESR measurements have been carried out in a temperature range of 10,300 K. A single, relatively broad and temperature dependent EPR signal was observed at all measurement temperatures. The linewidth slightly increases with decreasing temperature down to 100 K, then it sharply increases down to 60 K. Below 60 K the trend is reversed and the linewidth start to decrease. The resonance field remains almost constant down to 100 K and decreases sharply as the temperature is decreased further. The resonance field of the ESR spectra of Fe3O4 shows a linear dependence on microwave frequency. By using experimental results, the effective g-value and internal field are deduced as 1.9846 and ,40 G, respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Selective Inclusion of Electron-Donating Molecules into Porphyrin Nanochannels Derived from the Self-Assembly of Saddle-Distorted, Protonated Porphyrins and Photoinduced Electron Transfer from Guest Molecules to Porphyrin DicationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2007Takahiko Kojima Prof. Abstract A doubly protonated hydrochloride salt of a saddle-distorted dodecaphenylporphyrin (H2DPP), [H4DPPP]Cl2, forms a porphyrin nanochannel (PNC). X-ray crystallography was used to determine the structure of the molecule, which revealed the inclusion of guest molecules within the PNC. Electron-donating molecules, such as p -hydroquinone and p -xylene, were selectively included within the PNC in sharp contrast to electron acceptors, such as the corresponding quinones, which were not encapsulated. This result indicates that the PNC can recognize the electronic character and steric hindrance of the guest molecules during the course of inclusion. ESR measurements (photoirradiation at ,>340,nm at room temperature) of the PNC that contains p -hydroquinone, catechol, and tetrafluorohydroquinone guest molecules gave well-resolved signals, which were assigned to cation radicals formed without deprotonation based on results from computer simulations of the ESR spectra and density functional theory (DFT) calculations. The radicals are derived from photoinduced electron transfer from the guest molecules to the singlet state of H4DPP2+. Transient absorption spectroscopy by femtosecond laser flash photolysis allowed us to observe the formation of 1(H4DPP2+)*, which is converted to H4DPP+. by electron transfer from the guest molecules to 1(H4DPP2+)*, followed by fast disproportionation of H4DPP+., and charge recombination to give diamagnetic species and the triplet excited state 3(H4DPP2+)*, respectively. [source] | ||||||||||||||||